The goal of this Core is to enhance the definition of phenotype by providing histopathologic expertise coupled with modern methods of histopathologic analyses. The expertise provided by this Core will insure the application of appropriate tissue preparation, preservation, and interpretation of histopathologic materials. An additional feature of this Core is that it will provide a cooperative effort between veterinary pathologists who characterize the mouse lesions and human pathologists who understand the subtleties of the human pathologies and therefore can fit the model to specific subtypes. The evaluation of qualitative and complex traits, a subject of some of the proposals in this program project grant (PPG) will also be enhanced by this approach.